This invention includes embodiments that generally relate to a central core element for separator assemblies. In various embodiments, the invention relates to central core elements for spiral flow separator assemblies. The invention also includes methods for making separator assemblies comprising the central core elements provided by the present invention.
Conventional separator assemblies typically comprise a folded multilayer membrane assembly disposed around a porous exhaust conduit. The folded multilayer membrane assembly comprises a feed carrier layer in fluid contact with the active-surface of a membrane layer having an active surface and a passive surface. The folded multilayer membrane assembly also comprises a permeate carrier layer in contact with the passive surface of the membrane layer and a porous exhaust conduit. The folded membrane layer structure ensures contact between the feed carrier layer and the membrane layer without bringing the feed carrier layer into contact with the permeate carrier layer or the porous exhaust conduit. During operation, a feed solution containing a solute is brought into contact with the feed carrier layer of the multilayer membrane assembly which transmits the feed solution to the active surface of the membrane layer which modifies and transmits a portion of the feed solution as a permeate to the permeate carrier layer. The feed solution also serves to disrupt solute accretion at the active surface of the membrane layer and transport excess solute out of the multilayer membrane assembly. The permeate passes via the permeate carrier layer into the porous exhaust conduit which collects the permeate. Separator assemblies comprising folded multilayer membrane assemblies have been used in various fluid purification processes, including reverse osmosis, ultrafiltration, and microfiltration processes.
Folded multilayer membrane assemblies may be manufactured by bringing the active surface of a membrane layer having an active surface and a passive surface into contact with both surfaces of a feed carrier layer, the membrane layer being folded to create a pocket-like structure which envelops the feed carrier layer. The passive surface of the membrane layer is brought into contact with one or more permeate carrier layers to produce a membrane stack assembly in which the folded membrane layer is disposed between the feed carrier layer and one or more permeate carrier layers. A plurality of such membrane stack assemblies, each in contact with at least one common permeate carrier layer, is then wound around a conventional porous exhaust conduit in contact with the common permeate carrier layer to provide the separator assembly comprising the multilayer membrane assembly and the porous exhaust conduit. The edges of the membrane stack assemblies are appropriately sealed to prevent direct contact of the feed solution with the permeate carrier layer. A serious weakness separator assemblies comprising a folded multilayer membrane assembly is that the folding of the membrane layer may result in loss of membrane function leading to uncontrolled contact between the feed solution and the permeate carrier layer.
Recently, significant advances have been made in membrane separator assemblies for the reverse osmosis purification of fluids. These advances have been based in part on new central core element designs in which the central core element is configured to accommodate a first portion of a membrane stack assembly within a cavity the dimensions of which are defined independently by the central core element itself and not by the dimensions of the membrane stack assembly, nor by a transient relationship of central core element components to a fixed reference such as a holding jig. A second portion of the membrane stack assembly is disposed around the central core element to provide a separator assembly containing no folds in membrane components. Notwithstanding the promise of these new central core elements, significant challenges to their efficient manufacture remain. Thus, for example, the flow channels of the recently disclosed central core elements are characterized by deep interior volumes, and as a result central core elements comprising such flow channels are difficult to manufacture by injection molding since the mold tool used to create the flow channel must be withdrawn from the flow channel during the molding process. Withdrawal of a mold tool from a flow channel is especially problematic when the flow channel is non-prismatic with the exit cavity to which the interior flow channel is typically joined. The long and relatively thin mold tool tends to stick to the walls of the flow channel and, given the relatively large surface area of the combined interior surfaces of a typical flow channel of a typical porous exhaust conduit; it becomes difficult to withdraw the mold tool from the flow channel without damaging the molded part. A second challenge to the manufacture of the recently disclosed central core elements and their components is the tendency of the central core element components to warp during cooling. Non-uniform cooling and warping can be especially problematic when different portions of the central core element component have different wall thicknesses. In certain instances, the walls of a porous exhaust conduit must have different thicknesses in order to balance basic geometric limitations against the dimensional strength of the porous exhaust conduit needed to be useful. Thus, there exists a need for further improvements in both the design and manufacture of central core elements for separator assemblies. Particularly in the realm of water purification for human consumption, there is a compelling need for more robust and reliable separator assemblies which are both efficient and cost effective.